1. Field of the Invention
The present invention relates generally to the construction of atherectomy catheters for removing atheromas from a patient's arteries. In particular, the present invention relates to atherectomy devices using an inflatable balloon for effecting contact between an interventional implement and the atheroma.
Atherosclerosis is a condition characterized by fatty deposits (atheromas) in the intimal lining of a patient's arteries. Atherosclerosis can have many manifestations, including angina, hypertension, myocardial infarction, strokes, and the like. Initially, the atheromas deposited in the blood vessels remain relatively soft and tractable. Over time, however, the atheromas become calcified and hardened.
Atherectomy is a procedure which has been developed for removing atheromas from the vascular system, usually before substantial calcification has occurred. Atherectomy procedures utilize special catheters having a severing instrument located at a distal end thereof and, usually, an inflatable balloon located opposite the severing instrument. The catheter is positioned within the vascular system so that the severing instrument lies adjacent the atheroma, and the balloon is inflated to bring the severing instrument into close proximity with the atheroma. The severing instrument is then actuated to excise the atheroma, and the severed material captured to prevent the release of emboli.
The severing instrument on the atherectomy catheter can take a variety of forms, including fixed blades, (requiring movement of the entire catheter to effect cutting) and movable blades which can be actuated without movement of the catheter as a whole. Of particular interest to the present invention are atherectomy catheters having rotatable cutting blades which can be advanced across an aperture formed in a housing. The balloon is mounted on the housing so that the atheroma may be urged into the aperture with the cutting element being advanced to sever the atheroma. The use of the invention, however, is not limited to such cutting blades and applies to catheters having a wide variety of interventional implements mounted in a distal housing.
Heretofore, atherectomy devices have suffered from deficiencies in the manner in which inflation medium is supplied to the inflatable balloon. Atherectomy catheters generally require a torqueable shaft within the catheter body which allows the cutting head to be rotatably aligned with the atheroma after the catheter has been placed within the vascular system. Such torqueable shafts are typically formed from braided metal or other opaque materials which prevent viewing of the interior of the catheter. Thus, balloon inflation supply tubes which are inside the shaft are not visible, preventing examination for air bubbles. Air bubbles within the inflation medium are, of course, unacceptable as they could lead to air emboli should the inflatable balloon burst.
Additionally, the atherectomy catheters have suffered from problems in the sealing and joining of the inflation medium supply tubes to the inflatable balloon. As most atherectomy devices employ inflatable balloons which are separate from the tube or other member supplying inflation medium, a potential failure point is found at the junction between the inflation medium supply tube and the balloon. Moreover, the mechanical attachment of the balloon to the housing can be problematic.
Referring to FIG. 1 (prior art), the construction of an exemplary prior atherectomy catheter 120 is illustrated. The atherectomy catheter is of the type described in European Patent Application 163 502, the disclosure of which is incorporated herein by reference. Atherectomy catheter 120 includes a distal housing 122 secured to the distal end of a torqueable shaft 124. The housing 122 is axially and rotationally positioned within a patient's vascular system solely by manipulation of the proximal end of the catheter (not illustrated) with the torqueable shaft 124 acting to transmit all such motion.
The housing 122 has an elongate cutout 126 on one side thereof, and a rotatable cutting blade 128 is attached to the distal end of a drive cable 130. In use, the cutout 126 is urged against a region of atheroma by an inflatable balloon 132. Once the atheroma is within the cutout, blade 128 is driven using cable 130 to sever at least a portion of the atheroma.
Balloon 132 is inflated by an inflation tube 134 which is located on the outside of torqueable shaft 124 beneath a sheath 136. The sheath 136 will normally be constricted about the torqueable shaft in order to hold inflation tube 134 in place about the torqueable shaft 124.
Although a feasible construction, such placement of the inflation tube and inflatable balloon has several disadvantages. First, the small diameter of inflation tube 134 obscures the interior of the tube, masking any air bubbles which may be present. Second, the sheath 116 can cause constriction of the inflation tube 134, which can interfere with inflation of the balloon 132 under certain types of bending. Third, passage of the inflation tube 134 into the balloon is problematic. The tube 134 must pass beneath a clamping ring 140 which (together with a second clamping ring 140) holds the inflatable balloon 132 in place. The use of such clamping rings increases the likelihood that the inflation tube 134 may be constricted and further obscures visual examination of the tub for bubbles. Finally, use of the clamping rings 140 to secure the balloon 132 is problematic. The balloon 132 is held only at the ends, and the middle of the balloon has a tendency to roll away from the housing rendering positioning of the cutting blade 128 difficult. In alternate constructions (not illustrated), the balloon is attached to the housing by adhesives. Such adhesive attachment, however, can damage the fragile, thin-walled balloon material.
For the above reasons, it would be desirable to provide atherectomy and other interventional catheters where the entire balloon inflation system within the device is visible to the user while the device is being primed with inflation medium. Such visibility will allow the user to check for air bubbles which would endanger the patient should the inflatable balloon on the device burst during use. Additionally, it would be desirable to provide atherectomy devices having improved connections between the inflatable balloon and the tube or lumen supplying inflation medium through the length of the catheter. It would be particularly desirable if the balloon could be formed integrally (without joints) with the inflation medium supply tube or lumen. Finally, it would be desirable to provide such atherectomy catheters where the balloon were attached to the housing along its entire length so that the tendency of the balloon to roll away from the housing is minimized.
2. Description of the Background Art
U.S. Pat. Nos. 4,323,071 and 4,411,055 disclose balloon-tipped angioplasty catheters formed from inner and outer coaxial tube members. The outer coaxial tube defines the inflation balloon at its distal end and serves to carry inflation medium along the length of the catheter. U.S. Pat. Nos. 4,627,436 and 4,685,458 describe atherectomy devices which utilizes a fixed blade to sever atheroma. A lumen within the device carries inflation medium to a balloon located opposite the blade at the distal end of the device. U.S. Pat. No. 4,669,469 describes a single lumen atherectomy device where both a cutter cable and inflation medium pass through the lumen. The lumen is connected to the interior of an inflation balloon and the cutter cable is sealed by an O-ring. EPO 163 502 discloses an atherectomy device including a small diameter, discrete tube passing through a central lumen for providing inflation medium to an inflatable balloon. American Edwards Laboratories, Santa Ana, Calif., sells a balloon-tipped catheter having discrete inflation and vent lumens extending from the entire catheter length, as illustrated in sales sheet 132-8/86-LIS.